In any number of medical procedures it becomes necessary to deliver therapeutic material to an anatomic location. For example, it can be desirable to deliver materials usually as a fluid to particular locations within bone. This is particularly desirable when using bone screws. Materials such as calcium phosphate, hydroxyapatite, etc. are often needed to be delivered to aid in the fixation applied by an orthopedic screw.
Within the context of the present invention, which will be discussed in greater detail below, the inventors have discovered a method and apparatus which offer advantages over the currently known techniques. For convenience of explanation, the present invention will be described in conjunction with various applications, but principally bone screw and therapeutic material delivery systems. Various other applications and embodiments will be apparent in view of the following disclosure.
In the context of bone screws, bone screws may be applied to bone matrix for any number of reasons but usually such devices are attached for the purposes of repair of a weakened bone matrix in order to support bone or bone structure which has become fractured or weakened. In many cases, the fracturing of bone is in whole or in part due to disease. The bone breaks or weakens as a result of disease, for example, osteoporosis. Current techniques do not usually take into consideration that condition in the context of repair. The technique often used to repair bone may fail to address the situation under which the bone was fractured in the first place.
For example, in accordance with the conventional methods of attaching bone screws to bone, bone cement is injected through a pilot hole drilled into the bone prior to inserting the bone screw. After the bone screw is inserted into the site, the bone site theoretically hardens to strengthen the fixation site. This method lacks control over the location and the amount of bone cement applied. Often, difficulty in controlling the placement of a bone adhesive near tissues, specifically in the spinal cord region, allows improper placement resulting in injury. Too little bone cement or improper placement of the bone cement may result in a weak fixation site, which may lead to an undesirable extraction of the bone screw from the fixation site. For example, if the bone has been broken because of a chronic medical condition the use of cement in this fashion will not materially enhance fixation. Specifically, if the bone is weakened due to osteoporosis, then merely adding adhesive to the area may not necessarily address the pre-existing condition.